The present invention relates to a light control device configured to switch an optical path or limit it (i.e., to control the quantity of light) by displacement of a moving plate and consequently a mirror or light shielding plate mounted thereon.
FIG. 1A shows the construction of an optical switch which is an example of a conventional light control device of this kind. The illustrated optical switch is a 2-by-2 optical switch for switching optical paths of two incoming rays B 1 and B2 parallel to each other but opposite in direction.
On a moving plate 11 there are mounted four mirrors 12 as light control means. The mirrors 12 are disposed at an angle of 45 degrees with respect to the incoming rays B1 and B2, respectively, as depicted in FIG. 1A.
The moving plate 11 is supported by two support beams 13 in a manner to be displaceable in a direction vertical to the surface of the moving plate 11 itself. The support beams 13 are projected from a pair of opposed sides of the moving plate 11 of a square plate configuration, and are respectively extended around it along its three sides. The extended ends of the support beams 13 are fixedly coupled to stationary parts 15 on a frame 14 surrounding the moving plate 11.
Under the moving plate 11 is located a fixed electrode 16 at a predetermined spacing as shown in FIG. 1B, and a base 17 with which the fixed electrode 16 is formed integrally has its marginal portion joined to the frame 14. The moving plate 11 opposed to the fixed electrode 16 functions as a moving electrode.
In the optical switch of the above configuration, upon voltage application across the moving plate 11 and the fixed electrode 16, the moving plate 11 is attracted down by electrostatic power toward the fixed electrode 16, and upon removing the voltage, the moving plate returns to its initial position.
Accordingly, the optical switch is able to switch the optical paths by the mirrors 12 which undergo displacement as the moving plate 11 moves up and down. That is, when the moving plate 11 lies at the position indicated in FIG. 1B, the incoming rays B1 and B2 are reflected by the mirrors 12 to travel as indicated by the solid lines marked with the arrows, whereas when the moving plate 11 is at its lowered position, the mirrors 12 go out of the optical paths, allowing the incoming rays B1 and B2 to traveling in straight lines without being reflected by the mirrors 12.
FIGS. 2 and 3 show a sequence of steps involved in the manufacture of the above optical switch. The optical switch is manufactured using two base plates or substrates. Steps S1 to S4 in FIG. 2 show steps of processing the upper substrate, and steps S5 to S7 in FIG. 3 show steps of processing the lower substrate.
The upper substrate is, in this example, a multi-layered SOI (Silicon On Insulator) substrate 24 with a SiO2 layer 21 sandwiched between silicon (Si) layers 22 and 23 as depicted in FIG. 2. The manufacturing process will be described below step by step.
Step S1: The SOI substrate 24 are coated all over its top and bottom surfaces with thermally oxidized films 25 and 26, respectively.
Step S2: Patterns for the moving plate, the support beams and the stationary parts are formed by photolithography over the thermally oxidized film 25 on part of the top surface, then the thermally oxidized film 25 is selectively etched away as patterned, and the Si layer 22 is selectively etched away using the thermally oxidized film pattern as a mask. On the other hand, a frame pattern is formed by photolithography over the thermally oxidized layer 26, and the thermally oxidized film 26 is selectively etched away as patterned.
Step S3: The thermally oxidized film 25 remaining on the part of the top surface is etched away, and a thick resist film is coated over the entire area of the top surface and patterned to form mirror bodies, which are coated all over its surface area with an Au film to form the mirrors 12.
Step S4: The Si layer 23 on the side of the bottom surface is selectively etched away, and the SiO2 layer 21 is selectively etched away to form the frame 14. As a result, two stationary parts 15 are positioned on the SiO2 layer of the frame 14 composed of the Si layer 2 and the SiO2 layer 21, and the moving plate 11 carrying the mirrors 12 is supported by the stationary parts 15 through the support beams 13.
On the other hand, an Si substrate 27 is used as the lower substrate. Referring to FIG. 3, the manufacturing process will be described below step by step.
Step S5: The Si substrate 27 is coated all over its top and bottom surfaces with thermally oxidized films 28 and 29, respectively.
Step S6: A fixed electrode pattern is formed by photolithography over the thermally oxidized film 28, and the thermally oxidized film 28 is selectively etched away as patterned.
Step S7: The substrate 27 is etched away as predetermined using the pattern of the thermally oxidized film 26 as a mask, after which the thermally oxidized film 28 are etched away. As a result, the upwardly protruded fixed electrode 16 is formed on the base 17.
The Si substrate 27 and the SOI substrate 24 thus obtained are integrated into a single-piece structure with the frame 14 fixedly mounted on the base 17 by bonding, for instance. In this way, the optical switch shown in FIGS. 1A and 1B is manufactured.
In such a conventional a light control device as the above-described optical switch of the construction in which the moving plate is used as a moving electrode and displaced by electrostatic driving to switch or limit optical paths by displacement of the mirrors or light shielding plates mounted on the moving plate, the moving plate is drive in its widthwise direction, that is, in the direction vertical to the plate surface.
Accordingly, the fixed electrode for electrostatic driving of the moving plate needs to be disposed opposite the moving plate surface, but it is difficult to obtain from one substrate the moving plate (the moving electrode) and the fixed electrode bearing such a positional relationship to each other. On this account, it is conventional to produce them separately using two substrates and integrate them as by bonding.
Hence, the prior art manufacturing method involves patterning by photolithography and etching for each of the two substrate and necessitates their integration (by bonding) into a unitary structure; hence, these works inevitably increase the number of man-hours, making the manufacture of the light control device complicated and time-consuming.
It is therefore an object of the present invention to provide a light control device that can be manufactured with a smaller number of man-hours and with high accuracy.
The light control device according to the present invention comprises:
side beams;
a moving plate having opposed side surfaces;
at least one pair of support beams extended in opposite directions from said opposed side surfaces of said moving plate in parallel relation to said moving plate and having its tip ends fixed to said side beams, respectively, to support said moving plate in a manner to be elastically displaceable in a plane in which the plate surface of said moving plate lies;
drive means for driving said moving plate relative to said side beams in said plane in which said plate surface lies; and
light control means mounted on said moving plate, for controlling incident optical beams in accordance with the displacement of said moving plate by said drive means;
wherein said moving plate, said support beams, said side beams and said drive means are formed by etching one substrate.
Said drive means may be formed moving planar electrodes extended from sad side surfaces of said moving plate and a fixed planar electrode disposed opposite said moving comblike electrodes in common to them.
Alternatively, said drive means may be formed by moving comblike electrodes extended from sad side surfaces of said moving plate and a fixed comblike electrode disposed opposite said moving comblike electrodes in common to them.
The above light control device may have a construction in which: said paired support beams are extended from said side surfaces of said moving plate at a predetermined angle of inclination thereto and symmetrically arranged in respect to the center line parallel to the said direction of displacement of said moving plate; said drive means is disposed on either side of said moving plate in direction of displacement of said moving plate; and said paired support beams are driven by said drive means into snap action.
The above light control device may have a construction in which: said paired support beams are extended from said side surfaces of said moving plate at a predetermined angle of inclination thereto and symmetrically arranged in respect to the center line parallel to the direction of displacement of said moving plate; said drive means comprises plural sets of a thermally expansive member and an energy-conversion mechanism for converting thermal expansion of said thermal expansive member into a pressure in said direction of displacement of said moving plate, said drive means being capable of applying forward and backward pressures to said moving plate; and, on said moving member being pressed by said energy-conversion mechanism, said support beams performs snap action to drive and displace said moving plate.
The above light control device may have a construction in which: said light control means may be formed by mirrors to change optical paths of said incident optical beams; or said light control means may be formed by light shielding plates whose transmittance varies in the direction of displacement of said moving plate to control the amounts of incident optical beams transmitted.
Furthermore, in the above light control device said drive means may be formed by moving planar electrodes extended from said opposed side surfaces of said moving plate and a fixed planar electrode disposed opposite said moving planar electrode, or by moving comblike electrodes extended from said side surfaces of said moving plate and a fixed comblike electrode disposed opposite said moving comblike electrodes.
In the above optical control device, said substrate may be one of silicon layers of a multi-layered SiO2 substrate deposited all over its both sides with silicon layers, and grooves for fixedly receiving optical fibers may be cut in the other of said silicon layers.